Lower Endurance: Hardly an Issue

With perfect wear-leveling and write amplification of 1x, you would get 256,000GiB (that's ~275TB) of writes out of a 250GB Samsung 840 with TLC NAND and 1,000 P/E cycles. That is still a lot but wear-leveling and write amplification are never perfect. Giving any specific numbers for endurance is hard because every drive behaves differently and users have different workloads, but it's unlikely for a light consumer workload to see more than 10GiB of writes per day. That's 3,650GiB per year, which is only 1.4% out of 256,000GiB. In the real world NAND writes will be bigger than host writes but even with a write amplification factor of 10x, you will only end up writing 36,500GiB each year and exhausting ~143 P/E cycles out of the available 1,000. In other words, it would take roughly seven years for you to wear out the NAND.

SSD Lifetime Estimation

NAND

MLC—3K P/E Cycles

TLC—1K P/E Cycles

NAND Capacity

128GiB

256GiB

128GiB

256GiB

Writes per Day

10GiB

10GiB

10GiB

10GiB

Write Amplification

10x

10x

10x

10x

Total Estimated Lifespan

10.5 years

21.0 years

3.5 years

7.0 years

For the 120GB Samsung 840, the lifespan is half of the 250GB model but we are still talking about years. Samsung doesn't offer a 60/64GB Samsung 840, although that makes sense as it wouldn't be hard to wear that out in less than three years, which is the warranty Samsung gives to the 840 SSD.

DSP to the Rescue

However, there is actually more to SSD endurance than just P/E cycles and write amplification. There has been a lot of talk lately about digital signal processing (DSP) in the industry, which is supposedly the solution for lower endurance NAND.

The basic idea behind DSP is very simple: you read changes in voltages and adapt to the changes. As I mentioned in the previous page, the voltages change as the NAND wears out and if your controller can't adapt to the changes, you'll be stressing the NAND even more. Each time you're trying to program or erase the cell, you are wearing it out, so you don't even have to succesfully program or erase the cell to cause damage. That's why the guess and test process for writing to NAND is so harmful; it may take multiple tries and each try will wear out the NAND even more.

Graphical presentation of a change in voltage state

However, if your controller can read the changes in program and erase voltages, you will know what voltages to use to program/erase the cell. Even though DSP doesn't make NAND immortal, it causes a lot less stress on the NAND, allowing it to last for more P/E cycles than what you would get without DSP.

Again, it's hard to give out any specific numbers of DSP usefulness in real world, but for example STEC is claiming that their CellCare technology can extend the endurance of regular 3K P/E cycle MLC up to as much as 60K. I've heard unofficial figures as high as 100K for some companies' DSPs, but I would take all figures with a grain of salt until they are tested by a third party. Either way, even if a good DSP is only able to double the endurance of NAND, it's a huge deal as we move to even smaller process nodes and possibly even more bits per cell.

If Samsung 840 120GB cost's $109.99 and you can get an OCZ Vertex 4 128GB for $104.99, which is faster in 80% of the benchmarks and is $5 cheaper then who's going to want it? So what if the price goes down to $80, are people going to save $25 thinking their hard drive is going to die twice as fast. I have bought (with works money) around 30 ssd's including Intel 80GB & 160GB Silver Case, Intel 710 100GB, Vertex 3 Max IOPS 120GB and Vertex 4 128. So far I've only had 2 ssd's go bad and they were both Intel 80GB ssd's. One wouldn't power on and the other reported at 8MB. Intel replaced them under warranty.

The point is I have been buying SSD's for years and I just don't see how anyone would want these samsung ssd's. Samsung is famous for huge margins on each product. When a company pockets $240 off of a $500 tablet and their name isn't Apple then something is wrong.Reply

Wow, talk about skewing the data by cherry picking the worst-case numbers for the 840. The Vertex 4 is only 85% faster in one specific test: AS-SSD Write performance. Of course, in the AS-SSD Read performance it's also 10% faster than the Vertex 4 256GB, but you just ignore that? Samsung also has some of the best SSDs in terms of large reliability figures, so even if the 840 is slightly slower than other drives in some tests, it may be the better option. Also don't forget to factor in that the 840 appears to be well-tuned for light workloads (e.g it's near the top of our light workload results).

Personally, I think the 840 needs to come in below the current 830 drive prices to make sense, and it probably will not long after the official release. 128GB 830 drives already go for under $100, and 256GB drives have been at $200 for over a month now -- likely all in preparation for the release of the 840. TLC NAND is cheaper to manufacture (per GB), and long-term it will be significantly more profitable for Samsung. Get some good DSPs added into the mix and I wouldn't be surprised to see most SSDs in two generations being TLC based, with MLC moving to the enterprise level and SLC basically going away because it's too expensive.Reply

No I'm talking about counting each benchmark add the total and divide the number by how many OCZ Vertex 4 won and it was over 80% of the total number of benchmarks. How is Samsung a better option? TLC over MLC, OCZ fastest drive to Samsungs slowest new drive. Of course Samsung is going to make more profit but why would you want to spend the same amount on a slower drive with less endurance?Reply

If we look at average performance across all benchmarks, the difference between OCZ Vertex 256GB and Samsung 840 250GB is a 12.4% advantage for OCZ. However, OCZ hasn't exactly been free from firmware issues. That right there is the reason many people will pay a bit more for a Samsung (even if it's slower).

Would I buy an 840 right now for $200 or whatever? Definitely not -- I'd actually take the 830, just for proven reliability over time. Give the 840 a couple months just to be safe, then check the prices. If it's still more expensive than the Vertex 4, sure, go for OCZ if you'd like. If they're the same price, though, the 12% performance is practically meaningless for most consumer workloads.Reply

Because it's not just about performance, it's also about reliability. This is user data we are talking about. Even a single loss could be catastrophic. OCZ doesn't have the reliability track record that Samsung and Intel has, and for that reason there are many people who will only ever buy from Samsung or Intel. So then OCZ isn't even mentionable. It doesn't matter if they are faster because who cares if your data is at risk?

Also you have to consider that the REAL WORLD difference between any modern 6Gbps SSD is negligible, so then performance means even less. It ends up being a contest of reliability instead of a contest of speed. In that contest, OCZ loses. Reply

I would be buying an Intel instead if it cost $109.99. While Sammy is possibly the closest to intel in terms of reliability. I wouldn't want a TLC SSD for the same price. And the difference would be marginal anyway. I could feel the difference between a decent 3Gbps SSD and 6Gbps SSD, i am not sure if there is anything to feel for two decent 6Gbps SSD.

Now if the retail price is really in the range of $70 - 80 that would be a huge difference. Because you are essentially choosing the second best reliable SSD for decent performance and cheapest price. Reply